1. Field of the Invention
The invention relates to a microphone array with electromagnetic interference (EMI) shielding means.
2. Description of the Prior Art
FIG. 1 shows a conventional single microphone 100 used in various voice communication devices. The microphone 100 comprises an electret sensor 120 and an integrated circuit (e.g. J-channel field effect transistor, J-FET) 140 mounted in a housing 110. The electret sensor 120 comprises a diaphragm 121 and a back plate 122 both of which are permanently electrically charged to implement a capacitor. Incoming sound waves enter via a top opening 112 and are translated into mechanical vibrations upon contacting the diaphragm 121. The vibrations are converted into an electrical signal that varies in voltage amplitude and frequency corresponding to the original sound. The integrated circuit 140 receives and amplifies the electrical signal and provides an output signal. The integrated circuit 140 is mounted on a printed circuit board (PCB) 130 and is further coupled to external circuitry via openings 114 formed at the bottom of the housing 110. The housing 110 is made of metal serving as an electromagnetic interference (EMI) shielding means for protecting the integrated circuit 140 from EMI.
The described EMI shielding means, however, fails to provide full protection for a microphone array, which typically comprises at least two microphones mounted on a circuit board. External electromagnetic waves may penetrate through the circuit board affecting the integrated circuit therein.